A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. including part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
In the lithographic apparatus as hereabove specified, an article to be placed in the radiation beam is held to an article support, for example, by a clamping electrode by vacuum suction or otherwise. Electrostatic clamping may be used, for example, when a substrate is processed in vacuum conditions. This type of processing occurs, for example, when the type of irradiation used for photolithographic processes is in the (soft) x-ray region, also referred to as Extreme Ultraviolet (EUV) region. In current designs for wafer tables, wafer holders are often arranged in the form of a multilayer structure. Especially for electrostatic clamp designs, electrodes are buried in the structure so that a typical article support member set up is a thicker stabilizing layer of a rigid material, such as ZERODUR® glass ceramic material, a metal layer forming an electrode layer, and a top layer covering the electrode. Electrostatic clamping uses electrostatic attraction force as clamping force, which is typically dependent on a voltage difference and a clamping distance between the electrode and the wafer. In order to achieve good clamping, the applied voltage difference is high and the distance is small.
It has been found beneficial to reduce the distance in order to prevent excessive voltage differences, which may cause problems, such as breakthrough, etc.
A tendency exists to minimize the thickness of the covering layer. However, the covering layer that is applied on the electrode is often another rigid layer of a dielectric material, which may also have a specific structure of protrusions in order to minimize a surface for contacting the wafer. Thus, the covering layer may be very thin and, therefore, fragile in handling. Specifically, it has been found that the current thicknesses are often very vulnerable to contamination when the layers are bonded, because the contamination that is entrapped may amount to local stress in the top layer. This results in a top layer that is easily corrupted, and may cause, in the case of electrostatic clamping, occurrences of breakthrough. Otherwise, such contamination may destroy the flatness properties of the article support member, thereby causing undesired loss of resolution.
In the context of this application, the “article” may be any of the above-mentioned terms wafer, reticle, mask, or substrate, more specifically, terms such as a substrate to be processed in manufacturing devices employing lithographic projection techniques, or a lithographic projection mask or mask blank in a lithographic projection apparatus, a mask handling apparatus such as mask inspection or cleaning apparatus, or a mask manufacturing apparatus, or any other article or optical element that is clamped in the light path of the radiation system.